SAN FRANCISCO – Halfway across the San Francisco-Oakland Bay Bridge, an abrupt exit leads to Treasure Island, a seven-sided plain with spectacular views that inspire grandiose dreams. The Army Corps of Engineers created the island for the 1939 Golden Gate International Exposition, encircling 400 acres of bay shoals with rock walls, draining them, filling the void with sand and soil, and naming it after the famous adventure novel. Today, the city of San Francisco has set its sights on erecting a second downtown there.

But Treasure Island’s fate in the intervening decades—and a long-secret legacy of radioactive waste left behind—has complicated those plans.

After the exposition, the island was set to become a civilian airport—until the United States entered World War II. The Navy seized the land for the Treasure Island Naval Station and demolished the expo’s Art Moderne structures, leaving just the terminal and two hangars. In the spaces around them rose a little village of beige one- and two-story sheds.

For years, the base served its purpose until, in 1993, it landed on a decommission list. The military decamped, dismantling and cleanup began, and a few years later some former Navy housing was turned into city-subsidized rentals. By 2007, the Navy was well into the process of preparing the land for full transfer to civilian control.

That year, cleanup operations shifted from removing Navy industrial toxins and sludge to identifying any lingering radioactive waste. New World Environmental, a contractor working for the Navy, assigned specialist Robert McLean to conduct a preliminary radiation survey.

That was how McLean found himself cruising through neighborhoods built near former US Navy training academies, with a Ludlum radiation meter poked out of his truck window. He did not expect to find much; just the year before, a Navy-commissioned historical report had suggested there was little likelihood that significant radioactive waste would be found on the island. And by then, hundreds of San Franciscans were living in modest townhouses on Treasure Island and neighboring Yerba Buena Island–with the Navy’s assurances that doing so was perfectly safe.

Then, the sensor needle hopped.

“We picked up readings from inside the truck, without even getting out of the vehicle,” said McLean, speaking publicly about his discovery for the first time. That first detection was not the last.

“We found radiation, contaminated materials, in playgrounds and in areas that had previously been playgrounds,” said McLean, 52, who livesin North Carolina. “We found it in front yards. We found it underneath sidewalks and along the roadways.”

Months went by. With each new finding of radioactivity, it seemed the Navy would incrementally raise its estimates of how much waste might have been left behind on the island. McLean tried to blow the whistle, calling Kent Prendergast, radiation health division chief for the California Department of Public Health.

“McLean indicated that he was concerned regarding the fact that they are finding radium sources … at many locations on the west side of Treasure Island,” Prendergast wrote in an internal email dated June 25, 2008. McLean “was concerned that the sources could represent a hazard to children or something the bad guys could use to make a dirty bomb.”

McLean reported finding radium pieces that emitted enough radiation for a person at close range to receive, in an hour, five times the maximum radiation a nuclear worker is allowed to absorb in a year. Ionizing radiation increases cancer risks; eating or breathing traces of radioactive material can subject human cells to decades of bombardment that further raises those risks. In addition to the dangerously radioactive radium pieces, McLean’s readings showed that soil surrounding the objects was contaminated with traces of the material. Concentrations were not high enough to be certain people would be harmed, but such an unexpected discovery is supposed to prompt a thorough examination.

Instead, it prompted the bureaucratic equivalent of warfare, with state health officials on one side pushing for Treasure Island to be scoured more thoroughly for radioactivity and Navy officials and their contractors on the other, claiming there was no need.

In denying that a more sweeping assessment was warranted, the Navy denied its own Cold War history—a history largely kept secret for more than four decades, The Center for Investigative Reporting found in a yearlong investigation of radiation problems on Treasure Island.

For 46 years before the base was selected for closure, Treasure Island was home to nuclear war academies that used a variety of radionuclides in their training—including radium, plutonium and cesium 137—an in-depth review of military and government documents shows. The Navy knew for years that those materials were not always in safe hands. But the Navy did not acknowledge that history publicly, and as a result, cleanup crews and others preparing for redevelopment may have inadvertently spread radioactive material around the island.

Reporters from The Center for Investigative Reporting pulled proof of the island’s nuclear history from dozens of dusty boxes at the US National Archives in San Bruno, Calif., where visitors are advised to wash their hands before eating in case toxic residue remains in the files. It was uncovered from previously classified files housed at the National Atomic Testing Museum in Las Vegas and the Navy’s own archives. It was coaxed from the memories of those who have lived and worked on the island—and their survivors—and it was even unearthed from the soil on Treasure Island itself.

“What I saw at the birth of the Cold War and the testing program was this ignorance, arrogance, and secrecy, which combined into a hairy-chested attitude of, ‘If you can’t feel it, it doesn’t hurt you,’ ” Weisgall said. “As I’ve looked at the history ever since, that hairy-chested attitude continues to permeate the approach of government agencies that have dealt with the legacy of atomic weapons.”

The Center for Investigative Reporting asked the Navy to respond to allegations from state public health regulators that the military had botched the Treasure Island cleanup, providing Navy officials with public health department emails, memos, and military archival records underlying the allegations. Rather than address specific claims, the Navy responded with a blanket statement, asserting that officials have diligently sought to clean up Treasure Island:

“The Navy’s Environmental Restoration program is a data driven, iterative, step by step process with the goal of protecting human health and the environment,” the statement said. “All cleanup work continues to be conducted under rigorous State oversight with the highest priority given to safety to ensure the public is protected.”

Congress ordered a nationwide base closure program in 1988. For it to succeed, the military needed to expose its toxic and radioactive past, so crews could remove dangerous waste from areas slated to become new civilian homes and workplaces. But architects of the swords-to-neighborhoods plan vastly underestimated the military’s toxic and radioactive legacy—and its reticence to acknowledge it. In Northern California alone, that miscalculation has delayed and dashed a series of base redevelopment plans.

Across the Bay Bridge from Treasure Island lies the Hunters Point Naval Shipyard, where significant contamination from atomic weapon experiments and ship decontamination cost the government more than $800 million and held up development efforts for more than a decade.

Inland, officials at the former McClellan Air Force Base near Sacramento have dumped thousands of tons of radium-tainted soil on-site. Questions over who will end up owning the radioactive waste dump has led to tense relations with Sacramento city officials.

At the former Alameda Naval Air Station in the East Bay, plans launched in 2000 to build housing and commercial properties have stalled amid Navy environmental cleanup. It includes getting rid of radioactive residue washed off US jets that had scouted Soviet atomic tests.

On Treasure Island, McLean’s discovery and subsequent indications of radioactive contamination could have slowed down plans for a mixed-use urban mecca for some 20,000 residents. They could have touched off a systematic survey and scouring project. But that didn’t happen. Instead, the Navy fought back, even as it joined with the city in telling the 2,000 civilians already living on the island that they need not worry about exposure.

A history of mishandled radioactive material. Nicholas Kane attended a radiological training school on Treasure Island in 1948, its second year of operation. The training ship, the USS Independence, clearly left an impression on Kane, then 45 and an Air Force lieutenant colonel.

“It was scarred and twisted and misshapen from the atomic bomb tests at Bikini,” Kane wrote in a letter home. “I wandered across her warped flight decks.”

After Kane died of cancer in 1977, his daughter would receive official reassurances that any exposure he might have received during the classes he attended was “very low.” But the military’s message to Kane’s daughter, Sandra Marlow, might have been misleading. The Independence was one of more than 90 target vessels anchored at Bikini Atoll in 1946 to see how the atomic bomb tests of Operation Crossroads would affect them. The ship ultimately had been deemed so dangerously radioactive that it was sunk in 1951 off the coast of San Francisco, near the Farallon Islands.

The Independence and other target ships had been returned to ports up and down the West Coast, where they were decontaminated, dismantled, repaired or—in the case of the Independence—used as a classroom, records from the National Archives indicate. Even in those early years of the Atomic Age, some sailors on Treasure Island pushed back, protesting the risks of working around pools of water tinged with rust they believed was radioactive, according to 1947 military memos.

Treasure Island and the Marshall Islands are 4,600 miles apart, but the two were bound together by Operation Crossroads, which consisted of two atomic bomb tests that severely damaged Bikini Atoll’s ecosystem, contaminated hundreds of troops, and raised the Navy’s awareness of its own shortcomings. Target ships were drenched in radioactive fallout, and sailors didn’t know how to adequately protect themselves from radiation, declassified memos state.

A decade after the Bikini Atoll tests, the Navy built a full-scale mock-up of a 173-foot patrol craft on the west side of Treasure Island. To practice decontamination, sailors and other students would spray the mock-up, known as the USS Pandemonium, with short-half-life radioactive material, then scrub it off.

Inside the Pandemonium, 11 pieces of cesium 137 routinely were raised and lowered from lead enclosures so students could learn to use survey meters, according to a variety of sources, including a 1993 inventory of radiological materials and radioactive material licenses from the Atomic Energy Commission dating back to the 1960s.

On the east side of Treasure Island, the Navy built one-story classrooms that were used for radiation detection training. The dangerous nature of materials used inside was reflected in the design of the buildings. What Navy documents describe as “large sources” of plutonium, tritium, and cesium were contained in a corrugated steel classroom protected by a concrete wall that served as a “radiation shield and firebreak,” according to a 1982 base radiation safety memo.

Of course, the radioactive material used at Treasure Island training academies had to be disposed of when it was no longer needed. And the military did set up tracking procedures, but some of them fell far short of today’s standards. As a result, areas the Navy considered clean might not meet modern standards of radiation safety.

For example, the cleanup of a radium spill in a classroom in 1950 generated dozens of barrels of waste, which were dumped in the ocean near the Farallon Islands, according to internal Navy memos from that era, and the classroom area was deemed clean. But years later, surveys detected radiation emanating from under the classroom’s parking lot. Earlier this year, the site of that former classroom was an excavation pit, fenced off with radiation warning signs.

Another example of the evolution of radiation safety standards starts with a 1974 memo. Navy safety inspectors ordered that a plastic bag full of glow-in-the-dark radium pieces be “disposed of as required.” The Navy personnel manual from that era said such objects could be buried on-site. Today, standards call for packaging radioactive waste materials in strong, airtight, shielded containers and shipping them to secure radioactive burial sites.

Years later, workers involved in efforts to clean up the island for return to civilian control would uncover hundreds of radium pieces in former Navy waste pits and in the soil around military apartments built in the 1960s and ’70s. It’s unclear whether some were the pieces discussed in the 1974 memo.

In 2006, Navy contractors prepared a historical survey of radiation-related activities on Treasure Island. In it, the Navy emphasized that despite isolated mishaps, the Nuclear Regulatory Commission and the Navy’s Radiological Affairs Support Office carefully monitored radioactive materials during frequent safety inspection visits to the base.

The lengthy report didn’t mention one important fact: The Treasure Island atomic warfare schools were repeatedly chastised as a result of those inspections. According to audit reports, the Nuclear Regulatory Commission informed Treasure Island officials in 1978 that they had failed to follow radioactive safety protocols by, among other things, neglecting to routinely check sealed radiation sources that contained plutonium, cesium, and other materials for leakage. Two years later, the commission said the safety failures had not been corrected.

In 1984, the commission again reported that safety procedures weren’t being followed. The following year, auditors locked down facilities and suspended classes “pending correction of all safety related deficiencies,” according to an inspection report.

Navy radiation health physicist Roy H. Smith traveled from Virginia to Treasure Island in 1986 to take a look. He inspected the school’s radiac calibrators, radiation-beam-generating devices that measured radiation. He interviewed staff. In his report, Smith wrote that Treasure Island’s schools were so dysfunctional that they risked putting students in harm’s way and leaving the base’s trove of radioactive material insecure. Smith offered up reasons for the laxity: Navy officials at the school didn’t know how to use their instruments and demonstrated “a need for immediate remedial training in basic radiation physics and safety,” the report said.

Even after the base was selected for closure in 1993, outside audits continued to alert the Navy to a potential radioactive waste problem. In May 2001, six years before radiation testing by military cleanup contractors began, California’s Integrated Waste Management Board sent a letter to the Navy’s Treasure Island cleanup director, Jim Sullivan, warning that old garbage sites near base housing should be tested for radioactive waste. Records showed contaminants could have been scattered all over the housing area, the letter said.

Waste board staff “has brought this matter to the attention of the Navy,” the letter said, “but to date there has been no official response.”

The second of the operation’s two test bombs was detonated 90 feet underwater; it blew a funnel of radioactive water and coral dust into the sky, which rained down on the Bikini lagoon. Ships milled around in the soupy waters, their internal bilge pumping systems becoming encrusted with radioactive calcium fallout.

Some of the ships from this contaminated flotilla steamed from the Marshall Islands to the San Francisco Bay, where they anchored to be tested for radioactivity. Contaminated inside and out, they needed West Coast bases that could accommodate them—with piers and overhaul, salvage, and repair capacity, according to military memos stored at the National Archives. One such base was Treasure Island. Navy archives dating back to 1946 identify at least a half-dozen Operation Crossroads ships berthed at Treasure Island, in various stages of radioactivity.

More than a half-century later, Navy officials repeatedly reassured civilian residents that most atomic test ships docked at Treasure Island had been decontaminated. But in a once-secret 1947 Navy memo, officials discussed the “insufficiency” of ship decontamination. Radioactive ships were cleared for use, not because they were safe, the memo said, but because the Navy lacked a means to make them so.

The Navy revealed to Treasure Island residents in May 2012 that the former base had hosted ship overhaul and salvage operations, a possible source of radioactive waste. Sullivan, the Navy official who until a year ago oversaw base environmental cleanup at Treasure Island, downplayed the news.

“During a brief period during the latter part of World War II, there were salvage operations,” Sullivan said. “This wasn’t ship breaking or dismantlement. It was to provide support for other bases’ operations.”

State health regulators, however, still believed the Navy was not coming fully clean, according to internal memos. They began to fear this reticence accounted for the surprises cleanup contractors kept unearthing.

Seeking a thorough inspection. In 2010, Victor Anderson was nearing the end of a four-decade career as a physicist with the state Department of Public Health.

Anderson had heard about an unexpected detection of highly radioactive radium near occupied apartment buildings on Treasure Island. And he’d heard that a cleanup worker had been exposed to so much radiation that he was forced off the job.

That worker was Robert McLean, who, after working with radioactive material found under and around the apartment housing, had received radiation doses greater than allowed under his employers’ guidelines. He says he was fired on the grounds that he had not adequately protected himself from radiation that wasn’t supposed to have been there. The Navy told McLean’s employer, New World Environmental, to fire him or risk losing its contract, according to company President Don Wadsworth. “Under normal circumstances, he would not have been fired,” Wadsworth said. “But it is also true that he should have recognized the situation because of his training and avoided the total dose he received."

Of greatest concern to Anderson was one important fact: The Navy had not followed standard environmental cleanup industry procedures, which call for starting a cleanup by thoroughly surveying the entire property with sensitive instruments. The public health department had been assured Treasure Island wasn’t a significant radioactive waste site and didn’t require close scrutiny from Anderson’s specialized team.

On May 23, 2011, Anderson decided to double-check.

He made a relatively routine request of California’s other environmental contamination bureaucracy, the Department of Toxic Substances Control, asking for information about incidents on the island involving radioactive waste. He expected to get details about the discoveries by McLean and other cleanup workers and about why McLean had received excessive doses of radiation.

Instead, Anderson learned that management at the state toxics agency had ordered its employees not to deal directly with him and his colleagues, according to interviews and internal emails between Anderson and other government officials.

The Department of Toxic Substances Control is charged with monitoring environmental cleanup at Treasure Island. But the agency lacked expertise in radioactive material and was compelled to call in the health department’s radiation health experts. But Anderson believed the toxics agency wasn’t actually interested in letting members of his team ferret out information about mismanagement of Treasure Island’s radioactive cleanup.

In May 2011, the toxics agency’s Remedios Sunga rebuffed Anderson’s questions about McLean’s excessive radiation dose. In response, Anderson wrote: “Your reply is not very helpful or cooperative.”

That was among dozens of emails and memos from state radiation experts complaining their requests for information were ignored, blocked, or answered incorrectly. The two agencies were in the midst of a five-year flurry of dueling emails and memos about the cleanup. Anderson and some of his colleagues suspected the toxics agency was in too much of a hurry to clear the land for development as it sided with the Navy in resisting calls for a more thorough cleanup.

The Center for Investigative Reporting asked state toxics regulators for comment and shared dozens of emails among public health department staffers, in which health regulators criticized what they considered a cozy relationship between the military and toxics officials.The toxics department returned a brief response:“We value our working relationship with the California Department of Public Health on this project, and respect their contributions on the decisions that need to be made at Treasure Island. The steps that we have asked the Navy to take reflect CDPH’s input.”

One of the flashpoints in the duel between the state agencies came in January 2008, when the toxics agency asked the health department to sign off on a plan to allow civilians to live in areas where low-level radioactive waste was being excavated.

In a 1965 memo, an engineering firm evaluating land slated for Navy housing noted that it had been used as a garbage dump during an era when it was common to simply bury radioactive items. The memo said the area might be contaminated. During the 1960s and 1970s, the Navy had nonetheless built a cul-de-sac of sailor housing there.

After McLean’s 2007 discovery, specialists found radium contamination in people’s backyards, under carports, and in grassy common areas. Regulators and cleanup crews assumed the radioactive contamination extended under people’s apartments. But, according to internal emails, the Navy theorized that concrete floors would insulate residents from exposure.

The health department ultimately did not sign off on the plan for civilians to live at sites where radioactive waste had been found, according to a May 2008 internal memo. But that small victory contrasted with a general Navy intransigence.

Under normal cleanup protocol, the discoveries by McLean and others should have led to the bureaucratic equivalent of soul-searching. The Navy should have revised its 2006 historical radiation survey swiftly to incorporate the new knowledge. It should have complemented the historical research by scanning the island inch by inch to create a radiation road map. And it should have clearly communicated that process to civilians living on Treasure Island.

Instead, military officials continued to proceed as though the 2006 report were accurate, not updating it until 2012. Even then, the Navy failed to account for the base’s history of lax radiation safety or for dangers posed by ships irradiated at Bikini Atoll.

The infighting gets serious. Thousands of tons of dirt have been moved around on Treasure Island since a chemical waste cleanup began in 1999. Some was hauled away to other dumping grounds—without being tested for radioactivity. Three years ago, Kurt Jackson, a state radiation health specialist, raised an alarm. This created the potential for an islandwide radioactive mess, he wrote in an internal email to fellow health department physicists.

“We do not know what areas of Treasure Island have been contaminated,” Jackson wrote, adding that the Navy and its contractors have “moved soil around (Treasure Island) under their flawed conceptual model in open loaders and trucks without any apparent records of where soil not properly characterized for radionuclides may have been spilled.”

Anderson also considered the situation a public health threat. In a July 2011 email to his colleagues, he estimated a 1-in-20 chance that an object found by a member of the public would be radioactive enough to produce burns. “It is a matter of regulatory concern and public health and safety,” he wrote. “The department must take action as soon as possible to correct this problem.”

Anderson retired later that year and died in his sleep last March, at age 67. But others in the public health department also had been pushing for more scrutiny of the radiation situation on Treasure Island.

In December 2010, health department radiation specialist Gaetano Taibi and senior state health physicist Larry Morgan took an unannounced drive around Treasure Island. They found gates left open at radioactive waste cleanup sites and shared their concerns about it with the Navy. “Had we so desired, we could have driven into the excavation area, or exited our vehicles and walked directly into the … excavation area,” Taibi wrote.

A week after Taibi described the impromptu site inspection, a Navy lawyer contacted the health department to complain that “the drive-by was not coordinated with anyone and was simply opportunistic.”

The various agencies involved in the Treasure Island cleanup held a meeting—not so much to discuss preventing public access to dangerous areas, but to discuss health department violations of protocol. As a result, according to a December 20, 2010 memo, unannounced site visits were forbidden.

“Here’s what we expect moving forward,” Dan Ward, statewide military base cleanup manager for the state’s toxics department, wrote at the beginning of a letter ordering health department radiation experts to conduct no more surprise inspections.

“It was proposed to remove the radium data from the risk assessment document. The group literally broke out into laughter at that and there was instantaneous agreement that they would do that and simply reference it and put the information in a separate document,” Taibi wrote. “It was stated then the document would not have to go to CDPH (California Department of Public Health).”

Residents air health concerns. Like many sought-after American cities, San Francisco struggles with a shortage of affordable housing. So it seemed only logical to take advantage of the vacant Navy apartments on Treasure Island. Civilians were allowed to rent them under an interim program coordinated by the city of San Francisco to meet need while also offsetting site preparation costs. The views were spectacular, the rents reasonable.

The arrangement also was temporary, ending whenever the city was able to turn the land over to the private development consortium lined up to build new high-rises. Initially, plans called for a gradual phase out of the rental program to begin this year.

During the dozen years that civilians have lived on the island, the Navy has bombarded them with messages that the base cleanup was going smoothly, that the Navy’s 2006 report on the history of radiation on Treasure Island was correct, and that radioactive cleanup was an inconsequential side note to the chemical waste cleanup operation.

Every month, Sullivan—the Navy official who until last February oversaw the island cleanup—invited residents to a coffee-and-cookies meeting of the citizens’ Restoration Advisory Board, where he updated attendees, offering reassurances that the cleanup was proceeding safely and uneventfully.

For residents, the messages sometimes seemed to clash with reality. Radiation warning signs had come to seem as plentiful as street signs. Men in protective suits could be seen at fenced-in sites on the east, west and north edges of the island, toiling in ever-growing earthen pits, transferring dirt into special red metal shipping containers.

Kathryn Lundgren, who has lived on the island for a decade, recalled seeing men step out of an unmarked van and don the white suits in 2007: “booties, goggles, everything,” she said. The workers told her that they had permission from her landlord to come into her house and test for radioactive material.

The military finally updated its historical radiation report in 2012—acknowledging more of Treasure Island’s nuclear past—but that revision didn’t win the Navy many allies among island residents. Why, several of them asked, weren’t they warned before they chose to come and raise families there?

Lundgren and her neighbors banded into a group called the Treasure Island Health Network to press for yet more openness from the Navy. In September 2012, the Navy called a meeting. Dozens of residents showed up, many angry and afraid.

“We feel that you are all going home. We have to stay here,” Melanie Williams Jones told the assembled officials. “We need to know what’s going on.”

Residents described loaded trucks spilling dust along roadsides after leaving fenced-off areas posted with radiation warning logos. Vicki Jones complained about being exposed to dust from open trucks.

“My baby’s got a fungus in her head that the doctor can’t explain. She breaks out in bumps, but you guys don’t have answers,” she said. “I am so upset. I lay down at night and I say, ‘What’s next?’ ”

Fifty island residents contacted an Oakland law firm in hopes of joining a lawsuit. But the firm dropped the case for lack of evidence, said attorney Adante Pointer. While news of environmental contamination often triggers health complaints, it is exceedingly rare for epidemiologists to be able to prove a link between broad contamination and a specific person’s illness.

A dozen years ago, when media reports exposed undisclosed contamination at the former Hunters Point Naval Shipyard, three Democrats from Northern California stepped up, demanding answers from the secretary of the Navy. The Center for Investigative Reporting went to all three asking for their take on Treasure Island.

Democratic US Sens. Dianne Feinstein and Barbara Boxer did not respond. House Democratic leader Nancy Pelosi, whose district includes Treasure Island, responded through her spokeswoman, Evangeline George, who said in an emailed statement:

“Leader Pelosi’s office continues to closely monitor the cleanup process of the former Naval Station on Treasure Island, including proactively scheduling calls with the Navy, state Department of Public Health, and state Department of Toxic Controlled Substances. The Leader has a long history of fighting to secure cleanup funding in Washington for both Treasure Island and Hunters Point to ensure the Navy can clean up and turn over these properties so that they can be transformed into vibrant communities providing new jobs and additional housing—especially affordable housing.”

Uncovering cesium contamination. Cesium 137 is a radioactive byproduct of nuclear fission that is easily absorbed into muscle and other tissue, and such exposure can increase the risk of cancer. A cleanup worker who handled radioactive samples and testing offered The Center for Investigative Reporting a tip: The radioisotope could be found in a weedy lot on Treasure Island, just a pop fly away from a ball field and tennis court—even though that result had not shown up in thousands of pages of official Navy radioactive cleanup reports reviewed by reporters.

Development plans call for the area to be the future home of an apartment complex called Eastside Commons, along with ball fields, tennis courts, wetlands, and grassy play areas.

The lot includes two abandoned classrooms, areas declared clean enough for development in 2008. Still on the site are two barn-sized metal classrooms and a 300-square-foot walk-invault that was the target of a 1986 report, written by Navy radiation inspector Roy H. Smith, that suggested that Navy officials had handled dangerous radioactive materials, including cesium 137, without adequate knowledge of radiation safety procedures.

On a sunny day last March, debris from homeless encampments was strewn under the classroom buildings’ eaves, and holes in chain-link fences nearby offered easy public access to old equipment yards that are supposed to be off-limits.

In preparation for testing the area, two reporters from The Center for Investigative Reporting planted a grid of fluorescent-orange surveyors’ flags in the 6-acre field. The reporters carried a Ludlum sodium iodide detector, borrowed from a specialized radiation laboratory that had trained them to use it.

Four days of sweeping the detector over the site and digging from spots that showed elevated radioactivity produced 20 freezer bags of soil. A control sample was taken under a palm tree 50 feet from one of the classroom buildings.

The samples were sent to two certified radiation laboratories in California: New World Environmental in Livermore and Eberline Services in Richmond. The labs, each with decades of experience at military sites, were asked to test specifically for high levels of cesium 137.

The test results showed readings of cesium 137 as high as 0.315 picocuries per gram—up to three times the level previously acknowledged by the Navy and at least 60 percent higher than the Navy’s thresholds for environmental safety.

Those concentrations do not confirm a health hazard, according to Jan Beyea, a prominent nuclear physicist specializing in the health effects of low-level radiation. They are no greater than common contamination worldwide from 20th-century nuclear fallout.

But, Beyea said, the surprise finding in a location previously declared clean should prompt a more thorough evaluation of the island for potentially hotter spots.

“The fact that there is a level above standards is a clear mandate for further study and assessment of the extent of contamination and its origin,” Beyea wrote in an email, adding that more systematic testing is particularly important given that public play areas are planned nearby.

“Building a playfield is not an appropriate plan at this time,” he wrote, “given the tendency for little children to put things in their mouths.”

In emailed responses to the reporters’ questions, government officials suggested that the new information did not warrant action.

San Francisco’s Treasure Island development director at the time, Michael Tymoff, wrote that the city had “no basis to comment on the validity or accuracy of the tests.” The California Department of Public Health said it “does not comment on research conducted by others.” The Department of Toxics Substances Control said the agency would “determine what it means and where we go from here.”

“Such limited data taken out of context doesn’t provide much value,” wrote Keith Forman, the Navy’s Treasure Island cleanup coordinator.

On August 14, however, the Navy issued a letter asking radioactive testing contractors to bid on examining some areas of the abandoned lot surveyed by the center’s reporters—though not the spot where they found elevated readings. Contractors were to test for radium 226 and cesium 137.

The request noted the military’s expectations: “Contamination potential is low.”

Today, the Navy faces mounting public pressure to fully reckon with Treasure Island’s radioactive past. Responding to residents’ fears, city officials charged with turning the island over to developers last spring requested a special radiation survey near some of the apartments and duplexes.

As results came in, city officials sent a letter to island residents, saying low-level radiation found in the area did not pose a health threat. But the letter failed to mention one key finding: Radioactive shards, similar to those detected by cleanup worker McLean, had been discovered in public grassy areas near apartments. One small octagonal object was so hot that holding it for an hour could cause radiation burns, hair loss, and possible ulceration, according to an internal California Department of Public Health memo obtained via a public records request.

After The Center for Investigative Reporting wrote a story about the discovery in November, city and Navy officials downplayed its significance. But within two weeks, the city informed some residents that they’d be evacuated from their apartments. Their buildings needed to be razed for chemical cleanup, the notification said, not because of anything “related to ongoing radiological surveys.”

Two decades after the base was selected for closure, Ronald Pilorin, chief of the state public health department’s Emergency, Restoration and Waste Management Section, has escalated his agency’s campaign to make the Navy come clean about its radioactive past. In a November 8 response to the Navy’s assertion that Treasure Island’s neighborhoods were free from radioactive waste, Pilorin wrote that the military lacked credibility.

There had been “no credible effort made to gather evidence to determine whether those radioactive materials were present or not,” he told the cleanup project manager at the state Department of Toxic Substances Control.

“Assertions,” Pilorin said, “are not facts.”

Editor's note: This story was edited by Amy Pyle. It was copy edited by Nikki Frick and Christine Lee.This story was produced by the independent, nonprofit Center for Investigative Reporting, the country’s largest investigative reporting team. For more, visit www.cironline.org. The reporters can be reached at [email protected] and [email protected].